Hi
I also have a JB ATV 2. I haven't seen the icon for previous WWDC keynotes on there, so I've had to stream it from the website to iPad/iPhone and airplay to ATV2. This works fine.
I had the conference running on my Apple TV and watched portions of it when I was in the room. I was surprised that the video quality was quite good and it streamed smoothly, even though I have a very slow (2.4mb/s) DSL connection.